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Soft matter is a field of condensed matter physics that began to develop in France in the 1970s under the impulse of Pierre-Gilles de Gennes. I had the chance to participate in this adventure, and I describe in this article some of the memorable events. Soft matter is not only linked to physics but also to chemistry and biology, and working in this multidisciplinary field is quite stimulating. My particular expertise deals with liquid surfaces, an area that considerably expanded with the advent of miniaturization, i.e., when surfaces begin to matter. I was able to benefit from the French and European network systems, as well as from many interactions with young students and industrial partners. I show how these favorable conditions contributed to successes in my research.

Viscoelastic materials containing bubbles or drops are encountered in numerous application fields, and are presently the object of much interest. The motion of bubbles and drops in these matrices can be significantly different than in Newtonian fluids. This review is restricted to the case of motion in quiescent fluids (or small Reynolds number) and of small bubbles and drops, that are not appreciably deformed during their motion. It includes a brief description of properties of viscoelastic systems and of the motion of solid particles in these systems. The case of very small drops undergoing Brownian motion is related to recent advances in microrheology. The motion of larger drops and bubbles due to gravity in yield stress fluids is discussed and linked to Ostwald ripening. Recent advances on the understanding of the rheological properties of the composite systems are also briefly discussed.

The irreversibility of asphaltene adsorption at oil-water interfaces is still debated in the literature. We have used a Tracker instrument (Teclis) in which both liquid drops and bridges can be analyzed and interfacial tensions measured. Rinsing in the liquid bridge configuration is possible, making possible the study of opaque fluids. We confirmed that asphaltene adsorption is irreversible, for bulk concentrations below and above the CNAC, even at short times, when the interfacial layers are not yet consolidated. Despite working with a highly purified sample and avoiding part of the problems linked to the competition of different species for the interface, we did not observe significant differences in adsorption times and in the behavior upon compression with respect to asphaltenes with wider mass distribution.

International audience; It is prerequisite to characterize nanoparticles in dispersions in particular with respect to their size and size distribution before they can be used in toxicological testing. This requires robust methods with high reproducibility. The aim of this study was to apply interlaboratory comparisons using Dynamic Light Scattering (DLS), in order to evaluate the reproducibility of nanoparticle size determinations. DLS is well established in most nanotoxicological laboratories. Due to the fact that this technique appears easy to use it has become a standard technique nowadays. Still, reproducibility and in particular differences between different commercial instruments have not been addressed systematically before. Our aim was to develop a robust standard operating procedure (SOP). Therefore, at the beginning, experiments were performed with dispersions of rather monodisperse and spherical particles in water. Significant differences were observed between the results obtained with different commercial instruments for DLS, especially when fitting the data using mathematical inversion methods. As a consequence of the different settings applied when fitting the data, significant errors could be made especially when working with dilute dispersions of very small particles. Here we have identified options how to overcome possible issues. However, It should be noted, that in practice, nanoparticles may have significant polydispersities and/or be non-spherical. The potential of the DLS technique in this situation should be noted that in nanoparticles may have significant polydispersities and/or be non-spherical. The potential of the DLS technique in this situation is evaluated. A combination of two different techniques (DLS and electron microscopy for instance) is recommended to fully interpret the results.

We review the coarsening process of foams made with various surfactants and gases, focusing on physico-chemical aspects. Several parameters strongly affect coarsening: foam liquid fraction and foam film permeability, this permeability depending on the surfactant used. Both parameters may evolve with time: the liquid fraction, due to gravity drainage, and the film permeability, due to the decrease of capillary pressure during bubble growth, and to the subsequent increase in film thickness. Bubble coalescence may enhance the bubble's growth rate, in which case the bubble polydispersity increases. The differences found between the experiments reported in the literature and between experiments and theories are discussed.

There are still many open questions and problems in both fundamental research and practical applications of foams. Despite the fact that foams have been extensively studied, many aspects of foam physics and chemistry still remain unclear. Experiments on foams performed under microgravity allow studying wet foams, such as those obtained early during the foaming process. On Earth, wet foams evolve too quickly due to gravity drainage and only dry foams can be studied. This paper reviews the foam and foam film studies that we have performed in gravity-free conditions. It highlights the importance of surface rheology as well as of confinement effects in foams and foam films behaviour.

The water sorption behavior of representative pyridinium-based ionic liquid (IL), 1-hexylpyridinium hexafluorophosphate ([C6Py][PF6]), was studied over the whole range of the water activity a using a continuous gravimetric method. The analysis of the water sorption isotherm using the combination of a two-mode sorption (i.e. Henry-clustering) allowed to better understand [C6Py][PF6]-water interactions. At low and intermediate activity (a ≤ 0.8), the water molecules revealed a very low affinity to [C6Py][PF6] and, consequently, the water uptake was rather low. On the contrary, at high water activity (a > 0.8), the water uptake increased exponentially and the water clustering easily occurred. The constant of the Henry-clustering equation as well as the water clustering mechanism in [C6Py][PF6] were discussed and compared to those of imidazolium-based ILs: 1-hexyl-3-methylimidazolium hexafluorophosphate [C6C1im][PF6] (water-immiscible IL) and 1-butyl-3-methylimidazolium tetrafluoroborate [C4C1im][BF4] (water-miscible IL). It is shown that the sorption of water molecules by pyridinium-based ILs is controlled not only by the anion's nature, but also by the cation's nature. Moreover, the Zimm-Lundberg theory was used to determine the water mean cluster size (MCS) in [C6Py][PF6], [C6C1im][PF6] and [C4C1im][BF4]. The MCS results confirmed the strong capacity of water molecules to be aggregated in [C6Py][PF6]. In order to have a deeper insight into the water molecular state, infrared spectroscopy measurements were carried out as a function of the relative humidity value and the obtained results were correlated with the results of water sorption isotherms. It is found that at high water activity (a > 0.8), sorbed water molecules are strongly linked with ILs by hydrogen bonds and, therefore, are easily aggregated.

This short review describes the work on aqueous foam film stability with the important past contributions of Dotchi Exerowa and Dimo Platikanov, together with advances from other research groups. The review is focused on film rupture, for which few controlled experiments can be found in the literature and as a consequence, our understanding is still limited. The work on rupture of films in foams is described, together with the correlations with the rupture of isolated films. The review addresses mainly the case of aqueous films and foams, but analog studies of emulsions and emulsion films are also briefly discussed.

While coalescence is ultimately the most drastic destabilization process in foams, its underlying processes are still unclear. To better understand them, we track individual coalescence events in two-dimensional foams at controlled capillary pressure. We obtain statistical information revealing the influence of the different parameters which have been previously proposed to explain coalescence. Our main conclusion is that coalescence probability is simply proportional to the area of the thin film separating two bubbles, suggesting that coalescence is mostly stochastic.

We show that, while the gelation of colloidal silica proceeds much faster in the presence of added KCl than NaCl, the final gels are very similar in structure and properties. We have studied the gelation process by visual inspection and by small angle X-ray scattering for a range of salt and silica particle concentrations. The characteristic times of the early aggregation process and the formation of a stress-bearing structure with both salts are shown to collapse onto master curves with single multiplicative constants, linked to the stability ratio of the colloidal suspensions. The influence of the salt type and concentration is confirmed to be mainly kinetic, as the static structure factors and viscoelastic moduli of the gels are shown to be equivalent at normalized times. While there is strong variation in the kinetics, the structure and properties of the gel at long-times are shown to be mainly controlled by the concentration of particles, and hardly influenced by the type or the concentration of salt. This suggests that the differences between gels generated by different salts are only transient in time.

A central challenge for the safe design of nanomaterials (NMs) is the inherent variability of NM properties, both as produced and as they interact with and evolve in, their surroundings. This has led to uncertainty in the literature regarding whether the biological and toxicological effects reported for NMs are related to specific NM properties themselves, or rather to the presence of impurities or physical effects such as agglomeration of particles. Thus, there is a strong need for systematic evaluation of the synthesis and processing parameters that lead to potential variability of different NM batches and the reproducible production of commonly utilized NMs. The work described here represents over three years of effort across 14 European laboratories to assess the reproducibility of nanoparticle properties produced by the same and modified synthesis routes for four of the OECD priority NMs (silica dioxide, zinc oxide, cerium dioxide and titanium dioxide) as well as amine-modified polystyrene NMs, which are frequently employed as positive controls for nanotoxicity studies. For 46 different batches of the selected NMs, all physicochemical descriptors as prioritized by the OECD have been fully characterized. The study represents the most complete assessment of NMs batch-to-batch variability performed to date and provides numerous important insights into the potential sources of variability of NMs and how these might be reduced.

Nanoparticle in vitro toxicity studies often report contradictory results with one main reason being insufficient material characterization. In particular the characterization of nanoparticles in biological media remains challenging. Our aim was to provide robust protocols for two of the most commonly applied techniques for particle sizing, i.e. dynamic light scattering (DLS) and differential centrifugal sedimentation (DCS) that should be readily applicable also for users not specialized in nanoparticle physico-chemical characterization. A large number of participants (40, although not all participated in all rounds) were recruited for a series of inter-laboratory comparison (ILC) studies covering many different instrument types, commercial and custom-built, as another possible source of variation. ILCs were organized in a consecutive manner starting with dispersions in water employing well-characterized near-spherical silica nanoparticles (nominal 19 nm and 100 nm diameter) and two types of functionalized spherical polystyrene nanoparticles (nominal 50 nm diameter). At first each laboratory used their in-house established procedures. In particular for the 19 nm silica particles, the reproducibility of the methods was unacceptably high (reported results were between 10 nm and 50 nm). When comparing the results of the first ILC round it was observed that the DCS methods performed significantly worse than the DLS methods, thus emphasizing the need for standard operating procedures (SOPs). SOPs have been developed by four expert laboratories but were tested for robustness by a larger number of independent users in a second ILC (11 for DLS and 4 for DCS). In a similar approach another SOP for complex biological fluids, i.e. cell culture medium containing serum was developed, again confirmed via an ILC with 8 participating laboratories. Our study confirms that well-established and fit-for-purpose SOPs are indispensable for obtaining reliable and comparable particle size data. Our results also show that these SOPs must be optimized with respect to the intended measurement system (e.g. particle size technique, type of dispersant) and that they must be sufficiently detailed (e.g. avoiding ambiguity regarding measurand definition, etc.). SOPs may be developed by a small number of expert laboratories but for their widespread applicability they need to be verified by a larger number of laboratories., This work has been supported by the EU FP7 Capacities project QualityNano (grant no. INFRA-2010-262163).

The paper discusses adsorption and desorption energy barriers for macroscopic interfaces of surfactant solutions. Literature data suggest that adsorption and desorption are not always fully diffusion controlled. Apart from electrostatic barriers that lead to strong deviations, other types of barriers are less easy to identify, because smaller deviations from diffusion controlled mechanisms are evidenced. Complete models involving both diffusion and sorption barriers are very complex and involve many adjustable parameters, making the data analysis frequently unreliable. Empirical equations of state are used in most cases, although they are inaccurate, especially close to the cmc. The variation of sorption energies with surface concentration is not accurately described in the models. Finally, convection can mask the effect of sorption energy barriers. Experiments are presented to illustrate the main difficulties encountered.

We describe forced drainage experiments of foams made with model surfactant solutions with different surface rheology. We analyze the origin of two distinct drainage transitions reported in the literature, between regimes where the bubble surfaces are mobile or rigid. We propose that both transitions are related to the surface shear viscosity and to its shear thinning behavior. Shear thinning could also account for the huge discrepancies between measurements reported in the literature. The role of surface tension gradients, i.e. Marangoni effect, could not possibly explain the behavior observed with the different solutions.

We address the rheology of assemblies of surfactant-decorated silica nanoparticles irreversibly adsorbed at the gas/liquid interface. Positively charged surfactant molecules (such as CTAB) bind to silica nanoparticle surfaces, and the resulting particle–surfactant complexes adsorb at gas/liquid interfaces. The surfactant molecules control the wettability of such decorated nanoparticles and their adsorption. The interparticle forces can be tuned by changing the surfactant concentration Cs. Increasing Cs, in addition to a decrease of the particles wettability, leads to an increase of the area fraction of particles at the interface. Oscillatory shear measurements (strain- and frequency-sweep) have been performed. Here, we explore the effect of the surfactant concentration Cs. At high enough Cs, the interface is highly packed, and an overall solidlike response is observed, with 2D glass properties.

The gas permeability of the thin liquid films which separate neighbouring bubbles in a liquid foam plays a key role in foam coarsening. Different approaches have been developed in the past to measure the film permeability, relying on measurements either on individual films/bubbles or on bulk foams. While the first approach may not be sufficiently representative of a real foam film, the latter is hardly feasible due to a lack of quantitative description of the coarsening of bulk foams with non-negligible liquid content. Here we show that a good compromise between these approaches can be achieved by investigating the coarsening of quasi-two-dimensional foams. More precisely, we propose a particularly simple approach in which we follow the evolution of the number of bubbles of an initially monodisperse foam. In this case, a large number of bubbles disappear simultaneously, leading to a “catastrophic” event, which can be identified easily and accurately related to the film permeability. We demonstrate the potential of this technique by using aqueous foams stabilised by sodium dodecyl sulfate having different liquid fractions and containing different gases. The experiments are compared to Surface Evolver simulations.

When surfactants adsorb at liquid interfaces, they not only decrease the surface tension, they confer rheological properties to the interfaces. There are two types of rheological parameters associated to interfacial layers: compression and shear. The elastic response is described by a storage modulus and the dissipation by a loss modulus or equivalently a surface viscosity. Various types of instruments are available for the measurements of these coefficients, the most common being oscillating pendent drops instruments and rheometers equipped with bicones. These instruments are applicable to systems with large enough interfacial tensions, typically above a few mN/m. We use a new type of instrument based on spinning drop oscillations, allowing to extend the interfacial rheology studies to low and ultralow interfacial tension systems. We present examples of measurements with systems of high and low tension, discuss the possible artifacts and demonstrate the capability of this new technique. We emphasize that the data shown for low interfacial tensions are the first reported in the literature. The instrument is potentially interesting for instance in enhanced oil recovery or demulsification studies.

Supported ionic liquid membranes (SILMs) were prepared by immobilizing the room temperature ionic liquids (RTILs) ([C4C1im][BF4] and [CnC1im][PF6] (n=4 and 6)) in a porous Matrimid membrane. The Matrimid membrane was prepared by water vapor-induced phase inversion, and its porous structure was characterized by SEM. After immersion of the porous Matrimid membrane in RTILs, the prepared SILMs were composed of 60% of RTIL phase. From the bubble point test, the SILMs displayed an excellent retention of their RTIL phase, and thus showed a good stability in the face of increased pressure on one of their faces. The feasibility of the prepared SILMs for the separation of water and volatile organic compounds (VOCs) such as ethanol and cyclohexane by vapor permeation was investigated. For this purpose, a preliminary study of water and VOC vapor sorption in RTILs was necessary to determine the affinity between each solute and RTILs. Only [C4C1im][BF4] showed both the best sorption capacities and the good sorption selectivities. The vapor permeation measurements were therefore carried out only through the SILMs impregnated with [C4C1im][BF4]. The SILM permeability was found to increase in the same sorption affinity order as for [C4C1im][BF4], i.e. cyclohexane

Obtaining stable liquid foams is an important issue in view of their numerous applications. In some of these, the liquid foam in itself is of interest, in others, the liquid foam acts as a precursor for the generation of solid foam. In this short review, we will make a survey of the existing results in the area. This will include foams stabilised by surfactants, proteins and particles. The origin of the stability is related to the slowing down of coarsening, drainage or coalescence, and eventually to their arrest. The three effects are frequently coupled and in many cases, they act simultaneously and enhance one another. Drainage can be arrested if the liquid of the foam either gels or solidifies. Coalescence is slowed down by gelified foam films, and it can be arrested if the films become very thick and/or rigid. These mechanisms are thus qualitatively easy to identify, but they are less easy to model in order to obtain quantitative predictions. The slowing down of coarsening requests either very thick or small films, and its arrest was observed in cases where the surface compression modulus was large. The detail of the mechanisms at play remains unclear.

The surface functionalization of polyimide (Matrimid® 5218) films was carried out by cold plasma treatment with CF4, N2 and O2 gases using a radio frequency discharge and the optimum plasma conditions were evaluated by water contact angle measurements. The surface hydrophobicity of polyimide films was obtained after CF4 plasma treatment, while O2 and N2 plasma treatments contributed to the hydrophilic surface functionalization. X-ray photoelectron spectroscopy (XPS) results revealed the presence of CFx, amino or oxygen-containing groups attached to the polyimide film surface depending on the treatment gas. A strong influence of the used plasma gas on the film roughness was determined by atomic force microscopy (AFM) measurements. The influence of the surface modification on CO2, N2 and O2 gas permeation through the plasma treated films was evaluated. The permeation behaviour was characterized in terms of transport parameters, namely, coefficients of permeability, diffusion and solubility. The permeability coefficient of all plasma treated polyimide films for the studied gases (CO2, N2 and O2) was found to decrease following the order of increasing the kinetic molecular diameter of the penetrant gas. Besides, the selectivity coefficient was found to be significantly increased after the plasma treatments – αCO2/N2 was increased up to 36% and 98% for O2 and N2 plasma treated Matrimid® 5218 films, respectively. The relationship between the gas permeation behaviour and the surface modification of polymer film by cold plasma was discussed.

We have studied foams stabilised by surfactant-decorated nanoparticles adsorbed at the bubble surfaces. We show that the controlled compression of a single bubble allows one to understand the coarsening behavior of these foams. When bubbles are compressed, the particles become tightly packed in the surface layer. They lose their mobility, and the interface becomes solid-like when the jammed state is reached. Further compression leads to interfacial buckling characterised by crumpled surfaces. We find that the surface concentration of particles at which the jamming and the buckling transitions occur are independent of the surfactant concentration. This is a surprising feature. It suggests that the surfactants are mandatory to help the particles adsorb at the interface and that they change the equilibrium surface concentration of the decorated particles. But they do not affect the surface properties once the particles are adsorbed. We measured the compression elastic modulus of the surface in the jammed state and found it to be compatible with the Gibbs condition for which the spontaneous dissolution of bubbles is arrested. Due to this effect, the coarsening process of a foam composed of many close-packed bubbles occurs in two steps. In the first step, coarsening is slow and coalescence of the bigger bubbles is observed. In the second step, a number of very small bubbles remains, which exhibit crumpled surfaces and are stable over long times. This suggests that foam coarsening is arrested once the smallest bubbles become fully covered after the initial shrinking step.

Sigmoid-shaped isotherms for water vapor sorption in fuel cell membranes were analyzed with Feng's new dual-mode model for two series of ionomer systems, Nafion ® 117 membranes with different counter-ions and protonated Nafion ® membranes aged under different degrees of humidity. Feng's model appeared to be an excellent sorption model for these sigmoid isotherms and the values of its parameters were used for an analysis of the membrane structure/property relationships. The first model parameter, Cp , corresponds to the number of water molecules strongly sorbed in the first hydration shell of the membrane sulfonic sites. The upward curvature in the isotherms at high water activities, reflected by the A ′ parameter, appeared to be mainly due to the clustering of new water molecules on those of the first hydration shell. The number of water molecules per ionic site hydration depends on several structural parameters. The counter-ion of high electrostatic power attracts more water molecules per ion site, both in the first hydration shell and in subsequent sorption layers. The qualitative relationships between the membrane structure and its sorption properties obtained by analyzing the New Dual Mode Sorption (NDMS) model parameters make possible different interpretations of several data sets reported in the literature, such as the data on the sorption of different alcohols and the water sorption in Nafion ® membranes during ageing.

The characterisation of the dynamic properties of viscoelastic monolayers of surfactants at the gasliquid interface is very important in the analysis and prediction of foam stability. With most of the relevant dynamic processes being rapid (thermal fluctuation, film coalescence etc.) it is important to probe interfacial dynamics at high deformation rates. Today, only few techniques allow this, one of them being the characterisation of the propagation of electrocapillary waves on the liquid surface. Traditionally, this technique has been applied in a continuous mode (i.e. at constant frequency) in order to ensure reliable accuracy. Here we explore the possibility to analyse the propagation of an excited pulse in order to access the interfacial properties in one single Fourier treatment over a wide range of frequencies. The main advantage of this approach is that the measurement times and the required liquid volumes can be reduced significantly. This occurs at the cost of precision in the measurement, due partly to the presence of a pronounced resonance of the liquid surface. The pulsed approach may therefore be used to prescan the surface response before a more in-depth scan at constant frequency; or to follow the changes of the interfacial properties during surfactant adsorption., 17 pages,9 figures

International audience; Diffusing wave spectroscopy (DWS) was used to determine the size and volume fraction of nanoparticles (NP) within a foam taken as an example of a turbid media. The presence of two types of scatterers – dispersed NPs and liquid/gas interfaces – leads to two-fold dynamics in the system. Two characteristic decays of the temporal autocorrelation function are observed, their position and amplitude are dependent on particle concentration and foam age. Since only those NPs which are performing Brownian motion decorrelate the signal, one can follow the dynamics of particles' trapping into the foam matrix during the evolution of the system. This technique is a direct and noninvasive way to detect NPs in turbid media. The detection limit strongly depends on the NP nature and an algorithm for its estimation is provided.

a b s t r a c t We review here how millifluidic techniques can be used to construct versatile Labs-on-a-Chip, in which on-chip bubble generation and flow chemistry are efficiently combined to generate porous solids with highly monodisperse and ordered pore structures. With this approach, a liquid foam with well-controlled structural and chemical properties is first generated, which is then solidified in situ. We discuss here the interplay of various important processing parameters. In particular, we demonstrate that solidification time and foam life time need to be matched wisely in order to control precisely the properties of the final porous material. We also discuss a simple and inexpensive route to the manufacture of chemically and pressure-resistant, millifluidic Labs-on-a-Chip via the machining and hot-pressing of Cyclic Olefin Copolymers. We illustrate our review using the example of the generation of two types of hydrogel foams (synthetic acrylamide-based and biopolymer chitosan-based) and of particle foams, which may be used as green bodies for the manufacture of porous ceramics. The newly designed materials can be used to investigate fundamental questions of the structure-property relationship of porous solid. © 2012 Elsevier B.V. All rights reserved.

Much interest is being given these days to the development of techniques, which render liquid foams not only super-stable, but also responsive to non-contact stimulation. Both of these goals can be met simultaneously by the application of magnetic particles as stabilising agents, which not only suppress the traditional ageing mechanisms of foams (such as coalescence and coarsening), but also provide means of non-contact manipulation and characterisation by the application of magnetic fields. In this spirit we provide here detailed investigations into the use of commercially available MAGSILICA ® H8 nanoparticles, which consist of single-domain iron oxides surrounded by a silica shell, for the generation of super-stable bubbles and foams, and study their response to various types of magnetic fields. More specifically, we investigate the foaming behaviour of hydrophobic magnetic particles in water/ethanol mixtures for which we confirm that best foaming behaviour is achieved for intermediate wettabilities of the particles. We characterise the magnetisation of these foams and use magnetic field gradients to not only validate the super-stability of bubbles, but also to demonstrate the ease of their magnetic manipulation. Both kinds of measurements provide us with more detailed information on particle-detachment forces and the presence of a thick shell of aggregated particles at the gas/liquid interface. Last but not least, we demonstrate how such foams may conveniently be heated and kept at well-controlled temperatures through the application of oscillating magnetic fields.

Composite polymer membranes were prepared by incorporation of modified layered inorganic clay (Laponite) into Nafion® membranes. The modification of Laponite particles was performed by the plasma activation process and the chemical grafting of sulfonic groups as well as by the direct plasma sulfonation. The modified Laponite particles incorporated into a polymer film contribute to an increase of the proton conductivity of composite membranes at high temperatures (85 °C). For the first time the water vapor sorption properties of the modified clay and the composite membranes were investigated varying water activity conditions (from 0.1 to 0.95) by means of microgravimetry. The BET adsorption model as well as models of Park and Feng were applied to the experimental data. The parameter values (concentration of the adsorbed water, specific capacity and different aggregation constants) were found to agree well with the measured ones.

The adsorption kinetics of the cationic surfactant dodecyltrimethylammonium bromide at the air-water interface has been studied by the maximum bubble pressure method at concentrations below the critical micellar concentration. At short times, the adsorption is diffusion-limited. At longer times, the surface tension shows an intermediate plateau and can no longer be accounted for by a diffusion limited process. Instead, adsorption appears kinetically controlled and slowed down by an adsorption barrier. A Poisson-Boltzmann theory for the electrostatic repulsion from the surface does not fully account for the observed potential barrier. The possibility of a surface phase transition is expected from the fitted isotherms but has not been observed by Brewster angle microscopy., 13 pages, 5 figures

International audience; Single foam films made from mixtures of nonaggregated proteins and protein aggregates have been studied using a thin film balance apparatus. Their features (heterogeneity, stability and resistance to pressure change) are dependent on the aggregate size and on the ratio between nonaggregated proteins and protein aggregates. A phase diagram of these foam films has been drawn and a correlation of the structural properties of foam film and stability of real foams has been found. In particular, the formation of a gel-like network within the foam film coincides with the stability of the corresponding 3-D foams.

Poly(vinylalcohol) (PVA)/poly(ethyleneimine) (PEI)/poly(ethyleneglycol) (PEG) blend membranes were prepared by solution casting followed by solvent evaporation. The effects of the blend polymer composition on the membrane structure and CO2/N2 permeation characteristics were investigated. IR spectroscopy evidenced strong hydrogen bonding interactions between amorphous PVA and PEI, and weaker interactions between PVA and PEG. DSC studies showed that PVA crystallization was partially inhibited by the interactions between amorphous PVA and PEI blend, in which PEG separated into nodules. The CO2 permeability decreased with an increase in CO2 partial pressure in feed gas, while the N2 permeability remained constant. This result indicated that only CO2 was transported by the facilitated transport mechanism. The CO2 and N2 permeabilities increased monotonically with the PEI content in the blend membranes, whereas the ideal selectivity of CO2 to N2 transport showed a maximum. When CO2 is humidified, its permeability through the blend membranes is much higher than that of dry CO2, but the change in permeability due to the presence of humidity is reversible.

The review addresses the effect of geometrical confinement on the structure formation of colloidal dispersions like particle suspensions, (non)micellar surfactant solutions, polyelectrolyte solutions and mixed dispersions. The dispersions are entrapped either between two fluid interfaces (foam film) in a Thin Film Pressure Balance (TFPB) or between two solid interfaces in a Colloidal Probe Atomic Force Microscope (Colloidal Probe AFM) or a Surface Force Apparatus (SFA). The oscillating concentration profile in front of the surface leads to an oscillating force during film thinning. It is shown that the characteristic lengths like the distance between particles, the distance between micelles, or the mesh size of the polymer network remain the same during the confining process. The influence of different parameters like ionic strength, molecular structure, and the properties of the outer surfaces on the structure formation are reported. The confinement of mixed dispersions might lead to phase separation and capillary condensation, which in turn causes a pronounced attraction between the two opposing film surfaces.

Addition of surfactants to aqueous solutions of polyelectrolytes carrying an opposite charge causes the spontaneous formation of complexes in the bulk phase in certain concentration ranges. Under some conditions, compact monodisperse multichain complexes are obtained in the bulk. The size of these complexes depends on the mixing procedure and it can be varied in a controlled way from nanometers up to micrometers. The complexes exhibit microstructures analoguous to those of the precipitates formed at higher concentrations. In other cases, however, the bulk complexes are large, soft and polydisperse. In most cases, the dispersions are only kinetically stable and exhibit pronounced non-equilibrium features. Association at air-water interfaces readily occurs, even at very small concentrations. When the surfactant concentration is small, the surface complexes are usually made of a surfactant monolayer to which the polymer binds and adsorbs in a flat-like configuration. However, under some conditions, thicker layers can be found, with bulk complexes sticking to the surface. The association at solid-water interfaces is more complex and depends on the specific interactions between surfactants, polymers and the surface. However, the behaviour can be understood if distinctions between hydrophilic surfaces and hydrophobic surfaces are made. Note that the behaviour at air-water interfaces is closer to that of hydrophobic than that of hydrophilic solid surfaces. The relation between bulk and surface complexation will be discussed in this review. The emphasis will be given to the results obtained by the teams of the EC-funded Marie Curie RTN "SOCON".

Silver nanoparticles exhibit many interesting characteristics like optical properties and catalytic activities. Polymer membranes with in situ formed silver nanoparticles were prepared by dissolving together AgBF4 and poly- (amide 12)poly(tetramethyleneoxide) block copolymer in an organic medium then evaporating the solvent medium. UV-vis spectroscopic studies evidenced the formation in the solution of silver nanoparticles. The solid hybrid film changed its color with time under ambient conditions, indicating an evolution of the inorganic matters in the polymer matrix. The transmission electron microscopy showed nanoparticles whose size increases from 18 to 27 nm in the stabilized form in the polymer. The water vapor uptake in the membranes with different AgBF4 contents studied by microgravimetry allowed us to determine the sorption isotherms at 25 ∘ C. The sigmoidal BET-II type isotherms were fairly well fitted with Park’s equation, where the concave part was fitted with a Langmuir and a Henry sorption term, while the convex part was fitted with an exponential term in Park’s equation that takes into account the clustering of water molecules in the polymer matrix. We suggest that at low water activity, water molecules adsorb on Langmuir sites-probably on the nanoparticle surface-and at high activities water molecules form aggregates in the polymer matrix.

We studied the stratification behavior of free-standing foam films which are stabilized by nonionic surfactants and contain polyelectrolytes with different backbone flexibilities, namely sulfonated polyacrylamide (PAMPS), carboxymethyl-chitin (CM-Chitin), Xanthan, and DNA. Stratification is due to a specific arrangement of the polymer chains in the confined environment of the thin films. While stratification is easily observed for films containing PAMPS and CM-Chitin, it is more difficult to observe with Xanthan and DNA. We will discuss this effect in terms of different polymer backbone rigidities, which, in turn, are expected to lead to different time scales for polymer network relaxation.

International audience; By using simultaneously rheometry and a multiple light scattering technique, diffusing wave spectroscopy (DWS), we have studied the steady flows of three-dimensional aqueous foams. A number of parameters--the surfactants, the liquid volume fraction, and the roughness of the rheometer surfaces--are widely varied in order to determine which quantities have an impact on the macroscopic flow behaviors. By comparing to previous theoretical and experimental results, we show that flow regimes can either be slip or shear dominated. Two opposite slip regimes are identified; the transition from one to the other is obtained either by changing the surfactant or the liquid fraction, and we quantitately discuss which regime is selected for any given foam properties. Similarly, different shear regimes are also found, and we discuss the link between the macroscopic rheometry measurements, the nature of the flow, and the interfacial microscopic properties. Despite the occurrence of slip, we show how we can recover the actual shear rate by DWS, and how we can quantitatively explain the measured slip velocities.

Surface pressure versus specific molecular area (π–A) isotherms of stearic acid monolayers have been studied by varying the pH of the aqueous subphase containing monovalent (Na) or different divalent (Mg, Ca, Ba, Zn and Cd) cations. The lowering of the tilted to untilted phase transition pressure (πt) with increasing pH of the subphase is correlated with an increase of the headgroup dissociation of the acid monolayer. On pure water, the surface pressure drops after the collapse point (πc) to a lower pressure value (πl). The pressure-gap Δπ = πc − πl changes with increasing dissociation, depending upon the particular cation. After a certain pH, no pressure gap is observed and π remains constant or increases slowly after πc. This transition from constant area collapse to constant pressure collapse of the monolayer is observed for all monovalent and divalent cations near total monolayer dissociation.

The objective of this research work is the study of foams and emulsions stabilised by a protein, β-casein, and its relation to the dilatational properties of the adsorbed layers at the air–water and the oil–water interface. For this purpose, we have taken the dilatational properties of adsorbed layers at the air–water and tetradecane–water interfaces previously measured in Maldonado-Valderrama et al. [J. Maldonado-Valderrama, V.B. Fainerman, M.J. Galvez-Ruiz, A. Martin-Rodriguez, M.A. Cabrerizo-Vilchez, R. Miller, J. Phys. Chem. B 109 (2005) 1608–1616]. In order to facilitate the correlation, the interfacial coverage of bubbles and drops was chosen similar to that of the dilatational experiments. The formation and stabilising mechanisms of foams and emulsions obtained in this manner are discussed separately and linked to the dilatational properties of the adsorbed layers. The interfacial viscosity of the protein adsorbed layer appears to be a key factor in the formation of the foam whereas the interfacial elasticity seems to control both the stability of emulsions and foams. Moreover, a detailed comparative analysis of the different stabilising mechanisms and the corresponding dilatational properties is given.

A silicone-like membrane for vapor permeation was synthesized by deposition of tetramethyl disiloxane in a cold remote-plasma reactor onto a support. Although the chemical nature of the deposited polymer is similar to that of a conventional polydimethyl siloxane (PDMS) elastomer, except its higher inorganic silicon content, the morphology of the deposited layer is quite different. Polymer columns perpendicular to the surface were observed. Due to this, the dense plasma-deposited polymer, unlike the other elastomers, showed BET II-type sorption isotherms for organic and water vapors in the vapor-sorption measurements by microgravimetry. The first part of all isotherms can be well fitted with the dual-mode model for gas sorption, with a value of the Langmuir site capacity equal to 0.018 (volume fraction). The diffusion rates in the thin active layer were high compared with the vapor transport kinetics to the sample, so that the diffusion coefficient cannot be determined by vapor-sorption. An estimation of the diffusion coefficient from the steady permeation flux using the Long model confirmed the fast diffusion of vapors in the active layer (10−6 to 10−7 cm2/s). The sorption shows an anomalous behavior, which is reminiscent of a relaxation of the material structure during the course of sorption. The anomalous behavior, as well as the presence of Langmuir sorption sites in the elastomer, is attributed to the highly crosslinked materials in the zones at the boundary of polymer columns.

The electrostatic properties and the wetting behaviour of the human hair surface at the nanometric scale have been investigated by using atomic force microscopy (AFM). Surface potential imaging was used to determine the electrostatic properties while non-contact mode AFM was used to investigate the wetting properties of a test liquid, squalane. We have studied natural hair and hair in which different covalently (18-methyleicosanoic acid) and non-covalently bound fatty acids present at the cuticle surface were selectively extracted. This study shows how the removal of these acids causes various profound changes in hair wettability at the cuticle scale.

Composite materials are usually reinforced by synthetic fibers as carbon, glass etc…. Because of their good mechanical properties and low density, natural fibers are being considered more preferentially as reinforcement. The application of natural fibers as reinforcements in composite materials requires a strong adhesion between the fiber and the matrix. The poor resistance towards water absorption is one of the drawbacks of natural fibers which makes it more important to understand the dynamic properties of penetration of water molecules through these heterogeneous materials. Water vapour sorption kinetics in natural flax fibers have been performed at 25 °C by using an electronic microbalance (IGA, Hiden). By using the Fickian model for a complete cylinder water diffusion coefficients have been determined and calculated at short times (first half-sorption) and long times (second half-sorption) of kinetic curve and for different water activities. The values obtained for D1 and D2 are rather similar on the all range of water activity. Generally, water diffusivity increases and then decreases with water activity. The increase of diffusivity at low water activities may be explained on the basis of the dual mode sorption (Langmuir and Henry sorption’s combination) whereas the decrease for the higher activities can be attributed to the immobilization of sorbed water molecules due to the water clustering.

International audience; The 6th issue of OGST in 2015 collects individual contributions, at the difference of the other issues, dedicated to particular topics or to the proceedings of conferences held in IFP Energies nouvelles (IFPEN). The contributions to this issue have been classified into three groups: Enhanced Oil Recovery (EOR), asphaltenes and hydrates. EOR has been the topic of a specialissue in 2012: Challenges and New Approaches in EOR.

We review the existing literature on asphaltenes at various types of interfaces: oil-water, air-water, gas-oil and solid-liquid, with more emphasis on the oil-water interfaces. We address the role of asphaltene aggregation, recently clarified for asphaltenes in bulk by the Yen-Mullins model. We discuss the questions of adsorption reversibility and interfacial rheology, especially in connection with emulsion stability.

© 2015 American Chemical Society Ceramides have unique biophysical properties. Their high melting temperature and their ability to form lateral domains have converted ceramides into the paradigm of rigid lipids. Here, using shear surface rheology of egg-ceramide Langmuir monolayers, a solid to fluid transition was evidenced as a vanishing shear rigidity at lower temperatures than the lipid melting temperature. Such a mechanical transition, which depends on the lipid lateral pressure, was found in a broad range temperature (40-50°C). The solid to fluid transition was correlated to a LC to LC+LE phase transition, as confirmed by BAM experiments. Interestingly, together with the softening transition, a supercooling process compatible with a glassy behavior was found upon freezing. A new phase scenario is then depicted that broadens the mechanical behavior of natural ceramides. The phase diversity of ceramides might have important implications in their physiological roles.

The water sorption behavior for various RTILs ([C4C1im][BF4], [C4C1im][PF6], [C6C1im][PF6], [C4im][DBP], [C4im][BEHP] and [Et3HN][CF3SO3]) was studied over the whole range of water activity using a continuous gravimetric method. Analysis of the water sorption isotherms using the non-random two-liquid model (NRTL) and the combination of a dual-mode sorption (Henry-clustering) allowed a better understanding of the RTIL-water interactions. It is noticed that the sorption of water by RTILs is mainly controlled by the anion's nature. Anions interact with water molecules by hydrogen bonds that promotes the formation of a hydrogen bond network between the water molecules. The water uptake by RTILs increases in the following order (up to 0.8 in the water activity a): [C6C1im][PF6] ≤ [C4C1im][PF6] 0.8), water molecules are aggregated only in water-miscible RTILs (case of [C4im][DBP] and [Et3HN][CF3SO3]) because of their stronger anion basicity. To complete the sorption study, the molecular state of water dissolved in RTILs was studied by the infrared spectroscopy. The water molecules dissolved in water-immiscible RTIL such as [C4C1im][PF6] are not self-associated independently of the water content and, thus, can be defined as “free” water molecules interacting via H-bonding with the anions in the symmetric complex: anion⋯HOH⋯anion. On the contrary, the water molecules sorbed in water-miscible RTILs such as [C4im][DBP] or [Et3HN][CF3SO3] are strongly associated by H-bonds and also with the anions even at low water activity, and are easily aggregated when the water content reaches the critical concentration at high activity.

Ethylene/ethane sorption characteristics were determined for dry Pebax™ (poly(amide 12-block-tetramethylenoxide) copolymer)/AgBF 4 membranes by using an electronic microbalance. The membranes containing 0.7 and 22 wt.% AgBF 4 showed a dual-mode sorption isotherm. The ethane isotherms for all the membranes were of the Henry-type, which is the normal sorption for gases in rubbery polymers. The abnormal presence of Langmuir sorption sites only for ethylene in the rubbery copolymer, never reported sofar, is attributed to the silver-based specific complexation sites. The silver salt which dissolved in limited amounts in the rubbery copolymer had a much smaller Langmuir sorption capacity than the salt that crystallized in the copolymer. The sorption kinetics indicate that the crystallized salt did adsorb slowly ethylene according to a zeroth-order kinetics, but not ethane. The gas uptake kinetics resulting from a step of the pressure surrounding the copolymer exhibited one stage for ethane but two stages for ethylene. For the latter, there was first a fast Fickian sorption stage, then a drift of the zeroth-order sorption of ethylene on salt crystals, which contributes for a large part to the total uptake. The zeroth-order sorption suggests that the sorbed ethylene amount in the second-stage is independent of the crystal-surface coverage. The value of the Fickian diffusion coefficient calculated by fitting the kinetics with a solution of the second Fick’s law was 5 × 10 −12 m 2 /s for both ethylene (the first stage) and ethane, and is typical for small organic compounds in a rubbery material.

Poly(dimethylsiloxane) (PDMS)-HTiNbO5 nanocomposite membranes with various HTiNbO5 nanofiller content were prepared by melt intercalation. WAXS diffraction measurements and TEM observations have suggested that the HTiNbO5 mineral was exfoliated in the PDMS matrix. The influence of the filler in the membrane was evaluated by water diffusion, gas permeation (CO2, N2, O2, ethane and ethylene), toluene pervaporation and by CO2 sorption measurements. A filler content of only 2 wt.% in PDMS-HTiNbO5 nanocomposite membranes slows down the water diffusion significantly, and a filler content of 5 wt.% reduces also the permeability of the films for toluene. The addition of a filler content up to 10 wt.% do not significantly influences the gas permeability (P) except for CO2. The PDMS matrix appears to be highly permeable and, therefore, a decreasing effect on P is only marked for a very high HTiNbO5 content. This effect is more pronounced for CO2, the P value of which decreases by 80% when the amount of nanofiller is 40 wt.%. The sorption measurements show that the interaction between CO2 and PDMS is weak (isotherms agree with Henry’s law). The filler decreases the solubility of CO2 in the films (S = 7.94 × 10−3 and S = 5.44 × 10−3 cm3 STPcm−3 film cmHg−1 for PDMS and PDMS-HTiNbO5 40 wt.%, respectively).